1. Field of the Invention
This invention relates to a heat and flame resistant, flexible, insulating fabric. More particularly, it relates to a refractory coated porous base fabric. This invention especially relates to a heat and flame resistant coated porous base fabric employing an inorganic composition to bond the coating to the fabric.
2. Description of the Prior Art
Asbestos and other thermal protection materials are employed as protective mats for welding operations, furnace linings, fire-resistant linings and the like to provide protection from flames and thermal extremes as well as for dissipation of heat at a high rate. Although in each application reasonable performance is obtained, the selected material has limitations in its range of uses and in its effectiveness, even in uses for which it is particularly adapted. In addition, asbestos has found less utility in certain uses because of recent findings that it may constitute a health hazard.
Ceramics and/or glass fibers have been used heretofore to prepare high temperature electrical insulating tape. In addition, coated fabrics and ceramic structures have been prepared with a combination of glass fiber fabrics and metal oxides.
U.S. Pat. No. 2,587,916 of Squier discloses a heat-detecting cable of a pair of electrical wires separated by a glass composition containing barium oxide and/or boron oxide which is non-conductive at normal temperature but is conductive at high temperatures. In one embodiment, the glass is in the form of a fabric having finely divided refractory materials distributed therein to enhance the ability to withstand high temperature. The barium oxide and/or boron oxide containing fiberglass tape does not insulate the wires at high temperature but rather provides a conductive path so as to detect high temperatures.
U.S. Pat. No. 3,602,636 of Evans discloses an electrical cable where the conductors are helically wrapped with an open weave glass cloth having a coating of a flame resistant synthetic rubber together with an extruded sheath of polyvinylchloride (PVC) or the like covering the assembled cable.
U.S. Pat. No. 3,632,412 of Blance et al. discloses a pressure sensitive adhesive for a Class F (high temperature service) electrical tape. The adhesive is an interpolymer of acrylates, methacrylates and hydroxyacrylates or hydroxymethacrylates. Glass cloth is included among the useful backing members for this tape.
U.S. Pat. No. 3,013,902 of Bugosh discloses fabrics coated with colloidal alumina and a final coating of a polymer having a plurality of free carboxylic acid groups. Glass fibers are included in the list of materials which may comprise the fabric substrate. These textile products have improved resistance to soiling and improved washability.
U.S. Pat. No. 3,095,336 of Church et al. discloses the preparation of ceramic articles laminated with glass fabric by impregnating glass fibers with a mixture of a thermosetting resin and a ceramic filler, curing the resin, heating to gasify the resin and then heating to an elevated temperature to fuse the glass fabric and the ceramic filler to produce rigid, laminated ceramic structures having high strength characteristics.
U.S. Pat. No. 2,022,827 of Ruben discloses an impregnated textile or fibrous sheet useful as electrical insulation. The textile is composed of silk or cotton and is impregnated with a mixture of finely divided inorganic refractory materials in an organic binder plus an inorganic binder. The organic binder includes shellac, oleoresinous varnishes, phenol varnishes, rubber varnishes, oil-rubber varnishes or alkyl-resin lacquers. The inorganic binder is usually a boron compound although such materials as antimony oxide, zinc oxide, or ammonium phosphate may also be used.
U.S. Pat. No. 3,861,425 of Clark relates to a fibrous glass batting or board useful as an insulating material for the surfaces of heating and cooling ducts and, in particular, to a hardenable water base coating applied to the surface of this insulating material. The coating comprises an aluminum or magnesium hydrate, a vinyl acrylic latex binder and a fire retardant of sodium borate or boric acid.
Commonly assigned applications Ser. Nos. 073,362 and 225,888 and the recently-filed continuation-in-part application thereof disclose a heat resistant, flexible, refractory, insulating fabric composition of a porous base fabric, preferably a knitted fiberglass fabric, coated with heat resistant refractory materials, such as alumina and zirconia, and an organic bonding agent, such as acrylic latex alone or admixed with colloidal silica. A polymeric coating, such as polyvinyl chloride, may be formed over the coated fabric to provide abrasion resistance to the composition. A feature of this composition resides in the fact that the refractory materials are bonded in the interstices as well as to the surface of the base fabric, such that a significant amount of the fabric's flexibility and stretch properties are retained. This fabric composition has a variety of uses and therefore may be employed as the dielectric in insulated electrical wire or cable, as protective mats and curtains in welding operations, as linings for fire resistant machine and appliance covers, as duct and pipe insulation, as wrappings for engine exhaust systems and the like. When this fabric composition is exposed to heat and high temperatures, the organic bonding agent containing the refractory materials will decompose, causing the refractory materials to fuse into the softened surface of the knit fiberglass base fabric, enabling it to withstand intense heat and elevated temperatures well beyond the normal melt temperature of the fiberglass fabric. The resulting fabric structure will have ceramic qualities and will not soften, melt, drip or lose its insulating properties.
Although the organic components of the bonding agent of these prior art fabric compositions may not produce a flame when exposed to a flame or the intense heat developed by a flame, i.e. temperature of 1750.degree. F. and above, they will decompose at these temperatures resulting in some products of combustion in the form of smoke and fumes which may prove harmful to persons in the vicinity.
A heat resistant insulating fabric composition similar to those of the prior art but which does not emit products of combustion in the form of smoke and/or fumes would be desirable.
It is therefore an object of this invention to provide a heat resistant, insulating fabric composition which does not emit products of combustion in the form of smoke and/or fumes when exposed to flames and/or high temperatures.
It is another object of this invention to provide a method for preparing a heat resistant, insulating fabric composition which does not emit products of combustion in the form of smoke and/or fumes when exposed to flames and/or high temperatures.